1. Field of the Invention
The present invention relates generally to a slip control system for an automotive vehicle, which controls delivery of driving torque for a driving wheel for preventing the driving wheel from causing wheel slip. More specifically, the invention relates to a slip control system which adjusts engine speed upon occurrence of wheel slippage in excess of a predetermined magnitude, and which is provided better transition characteristics in switching engine control mode from slip control mode and normal engine control mode.
2. Description of the Background Art
Japanese patent First (unexamined) Publication (Tokkai) Showa 60-104730 discloses an automotive slip control system in which fuel cut-off is performed in a slip control mode operation which is initiated in response to the occurrence of wheel slippage in excess of a predetermined magnitude. Fuel cut-off is selectively performed for all engine cylinder and limited number of engine cylinder depending upon the engine speed at the occurrence of the excessive wheel slippage. By performing fuel cut-off, output torque of the engine is reduced for recovering road traction of the driving wheel.
However, such prior proposed wheel slip control system determine the timing of initiation and termination of slip suppressive fuel cut-off operation simply based on wheel slip threshold level which is determined on the basis of the speed of the driving wheel and driven wheel. Variation of rotation speed of driving wheel tends to lag in acceleration and deceleration of the engine, due to distortion of a propeller shaft, lag in a torque converter of an automatic power transmission and so forth. Such lag in variation of the driving wheel rotation speed tends to cause delay of resumption of fuel supply. This causes excessive deceleration of the engine which deceleration of engine is due to distortion of a propeller shaft, leg in a torque converter of an automatic power transmission, and so forth. Such lag in the variation of the driving wheel rotation speed tends to cause delay of resumption of fuel supply. This causes excessive deceleration of the engine which brings engine stall in the worst case.